The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, speed ratios of an automatic transmission or a manual transmission are fixed to constant values, and are controlled depending on driving conditions. On the other hand, a continuously variable transmission (CVT) enables speed ratios to be continuously changed within a predetermined range.
Ride comfort and acceleration performance are excellent and fuel consumption is low according to the CVT since shifting is achieved only by operating an acceleration pedal. In addition, the CVT may reduce production cost since the CVT has fewer components, compared with an automatic transmission.
However, in a CVT that is controlled by hydraulic pressure, oil viscosity is increased when the temperature of the oil is low in a low temperature region of an engine applied to the CVT, so a fluctuation of oil pressure supplied to the CVT may be strong when the viscosity is high. Therefore, if a region in which the oil pressure is lower than a required pressure exists depending on an amplitude of pressure fluctuation, the CVT may be damaged or fail as tension of a belt is not maintained.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.